The invention relates to an active compound chip having an integrated heating element for evaporating active compounds from the active compound chip. The invention furthermore relates to a process for the production of an active compound chip having an integrated heating element.
Various devices for the evaporation of active compounds such as insecticides or fragrances are known.
A device suitable for this purpose is a plate evaporater, consisting of a heating apparatus and insecticide plates. The insecticide plates consist of materials such as cellulose or cotton board, asbestos or ceramic and are impregnated with pyrethroid insecticides. The insecticide plates are placed on the heating apparatus, which can typically generate a temperature in range from 120 to 190° C. The insecticides are evaporated from the plates by the heat of the heating apparatus. The duration of action with plate evaporators is restricted to approximately 12 hours because of the high working temperature and the uneven release of active compound.
A similar principle underlies the gel evaporator (DE 197 31 156 A1 ), in which insecticides are incorporated into a gel formulation.
Another possibility for the evaporation of active compounds consists in the use of “liquid evaporators”, in which a liquid formulation of the active compound is continuously evaporated by warming by means of a wick system (GB 2 153 227).
Polymeric active compound carriers, into which insecticidal active compounds are incorporated, are known from DE 196 05 581 A1. These polymeric active compound carriers theoretically have a working temperature of 60 to 150° C. In practice, however, it has been shown that a continuous rate of release of the active compound over a period of time of up to 60 days in a biologically active amount can only be realized using a large surface which is impracticable for the application or using a temperature in the range from 140 to 150° C. For the evaporation of the active compound, the polymeric active compound carriers are placed on a heating apparatus, such as is already known for plate and gel evaporators. Tests have shown that in the range from 110 to 100° C. the release rate of the active compound and thus the biological activity greatly decreases.
All known evaporator systems need an external heating apparatus in order to generate the heat necessary for the evaporation of the active compound. Such a heating apparatus causes additional expense and needs a certain space at the site of application. Moreover, it leaves room for faulty operation. If, for example, a controllable heating apparatus is concerned, a wrong temperature adjustment can lead to over- or underdosage of the active compound. If a controllable heating apparatus is not concerned, different heating apparatuses must be bought for the evaporation of active compounds having different evaporation temperatures.
A disadvantage of the known evaporator systems is furthermore the low efficiency caused by the heating apparatus. The heat transfer between the heating apparatus and the active compound carrier is poor, since complete contact between the surfaces of active compound carrier and heating plate is not achieved and an insulating layer of air can form between parts of the active compound carrier and the heating apparatus. This leads to the fact that it takes a long time until the active compound carrier is warmed so strongly that the active compound evaporates. High temperatures of the heating apparatus are needed in order to evaporate the active compound in an amount which is necessary, for example, for the effective control of insects. These high temperatures also border on the housing, so that there is a danger of burning for the user. At high temperatures, there is also the danger that other parts of the active compound formulation than the active compound itself evaporate and contribute to unnecessary pollution of the environment.
The poor heat transfer furthermore leads to incomplete liberation of the active compound from the active compound carrier. In the case of polymeric active compound carriers which had been heated on a heating plate, a residue of up to 20% of active compound was measured in the active compound carrier.
On account of the poor heat conductivity of the polymers and possibly occurring deformations of the active compound carriers, exact temperature control is not possible, so that uneven escape of active compound can occur.
The known systems have the further disadvantage that the non-heated surfaces of the heating apparatus, in particular, are in some cases so cool that the released active compound immediately condenses on them again.